Stars Stars are classified by spectral classes O,B,A,F,G,K,M Oh be a fine girl (or guy), kiss me! Key here is the effective temperature of the star (surface temperature) Difference in spectrum is due to temperature on the surface of the star See color spectrum of O,B,A,F,G,K, and M in the image to the right ->
Stars For Jupiter: M/Msun = 0.001
Special classes (Right Now!) R-class stars Stars Like K-class except lots of carbon N-class stars Like M-class except lots of carbon S-class stars Like M-class except with zirconium oxide and lanthanum oxide bands WN and WC are Wolf-Rayet stars Like O-class except carbon and nitrogen emission lines (strong)
We can determine some characteristics of stars using simple physical law Distance Stars Discussed in lecture 3 Standard candle (Cepheid Variable) Temperature Wien's Law Spectral Class Luminosity Use inverse square law and apparent brightness Class of spectrum
Stars Stellar spectrum can look different for the same spectral class of stars Some have broader lines then others This means different properties in the same spectral class To resolve this another class was developed Luminosity Class Same temperature Different luminosity
Stars The Hertzsprung-Russell Diagram (H-R) Grand graph that relates spectral class, luminosity, temperature, mass, size, etc. Useful for understanding stars evolution Majority of stars are in the main sequence Our own Sun
Stars Another example of the Hertzsprung-Russell Diagram (H-R) Wikipedia's example Here you see the different stars as points Note the majority (~90%) of points are in the main sequence
Stars The spectral temperature luminosity graph is like a Hertzsprung-Russell Diagram (H-R) but is usually for smaller samples like a cluster or galaxy Wikipedia's example Similar to HR diagram, but is different and requires a conversion from one to another
Stars Important to the H-R diagram Apparent magnitude What we see Dimmer if further away Absolute magnitude Total energy output per second Apparent magnitude if the object is 10 parsecs away Parsec is about 3.262 light-years
Stars Periodic gives absolute magnitude With absolute magnitude and apparent magnitude can figure out distance of stars As objects get more distance their brightness will dim Inverse square law
Betelgeuse (example star) Betelgeuse Alpha Orionis (in Orion) (Arabic derived name) Red massive supergiant Nearing end of life Will be a supernova If this star was in our solar system it surface would be passed Jupiter Image is the first of a surface of a star other than our sun (~2010) Interferometry was used to get this image Other star s surfaces have been imaged since
Betelgeuse spectrum Betelgeuse spectrum Upper end of spectrum By Raymond Gilchrist - The spectrum appears on a website entitled, "Betelgeuse Graph and Spectrum" https://www.fas.harvard.edu/~astrolab/spectrabetelgeuserigel_spu21.html
Example Stars Antares Red supergiant One of brightest stars in the sky In Scorpius (Alpha Scorpii) Nebula around the star was expelled by Antares Companion blue star Lower left corner Also shown Rho Ophiuchi (star with blue surrounding it) and Sigma Scorpii (Cephei-type star with red surrounding it)
Example Stars Canopus One of brightest stars in the sky In Carina (Alpha Carinae) Supergiant
Example Stars Aldebaran In Taurus (Alpha Tauri) Means the follower from Arabic because if follows the Seven Sisters across the sky Giant Could have solar system
Example Stars Mira Red Giant Star Companion is a white dwarf star possibly causing the strange perturbation in the picture
Example Stars Sirius B White Dwarf Companion to the brighter Sirius-A Not known until 1862, however predicted by the motion of Sirius-A Diameter 8400 km (smaller than the Earth, however as massive as the Sun)
Example Stars (Main Achenar (in Eridanus) Derived from Arabic Alpha Eridani Blue-white Oblate Star...spins very rapidly! Bright star, but in the Southern Hemisphere... sequence)
Example Stars (Main Altair (Atair) In Aquila (Alpha Aquilae) 12 th brightest star Oblate because of rapid rotation White star sequence)
Example Stars (Main Barnard's Star In Ophiuchus Large proper motion Discovered by E.E. Barnard Red dwarf Flared in 1998, so might be a flare star Sequence)
Example Stars (Main Proxima Centauri Red Dwarf Flare Star Nearest star to the Sun Part of Alpha Centauri system Sequence)
Evolution of a star (quickly) Interstellar medium (dust) Contraction of the Cloud Proto-star Young star Medium star Mature star (contracts almost all helium now) Red Giant Helium Flash Helium Star Bye-Bye White Dwarf (small stars) Supernova (medium to large stars) Remnants may become black dwarfs Or black holes